A typical example for a network is a fault-tolerant time-triggered network comprising at least one communication channel to interconnect at least two network nodes. Such fault-tolerant time-triggered networks are widely used in the automotive area. A star network includes a star coupler and at least two network branches, wherein each network branch at least includes a network node. Such network node could be a sensor or an actuator in such automotive network, wherein information sensed by the sensors needs to be reliably transmitted to the actuator. To increase the safety of cars using such automotive networks the requirements in respect to fault robustness are very high. Moreover, the increasing number of electronic equipment in modern cars requires a well defined behavior of the network independently of the status of single components of the network.
As already mentioned such network includes a plurality of network nodes, wherein each network node includes a bus driver, a communication controller and an application host. Optionally, a network node could include a bus guardian device for further increasing the fault robustness. The bus driver transmits information provided by the communication controller via an output channel to the other network nodes. In turn, the bus driver provides information to the communication controller received via an input channel from the other network nodes. This information is included in data and control symbols, both comprising data bits. In other words, the communication controller is connected to the input and output channel via the bus driver. The communication controller delivers relevant information to and receives information from the application host, and assembles data frames based on the received information for delivering to the bus driver.
Now, the interconnection of the network nodes in the network is described in more detail. All network nodes are interconnected by a predetermined network topology. In the following, a star topology and especially an active star topology will be of interest.
A simple example for an active star topology is to connect all network nodes via a point to point connection to an active star coupler. That is, a simple active star network comprises the active star coupler and the network nodes, which are interconnected respectively to the active star coupler by a point to point connection. The active star coupler receives information from one network node and forwards the information to all other network nodes.
Another example for an active star topology is a cascaded active star topology, in which two single active star networks are connected via a single point-two-point connection.
A further example for an active star topology is a so-called ‘hybrid’ topology. Therein, also passive busses interconnecting a plurality of network nodes can be connected to an active star network.
The star coupler is one of the core elements of a star network. Each connection point of an active star coupler could be connected to a single network node or a whole sub-network of an arbitrary network topology. A network node or a sub-network connected to a star coupler is called network branch.
Now, the active star coupler of the active star network is described in more detail. Usually the active star coupler is not only responsible for performing forwarding functions. However, it may happen that network nodes of two different network branches simultaneously try to transmit information to the active star coupler. In such case, the active star coupler may be adapted to resolve those situations. Further, bit-reshaping or signal regeneration capabilities may be incorporated into the active star coupler. The active star coupler comprises a plurality of bus drivers interconnected to each other. That is, in a most basic form, a simple logic interconnects these bus drivers to an active star network.
The bus drivers of the active star coupler may also perform simple fault detection functions, as described for example in “FlexRay, Communication Systems Electrical Physical Layer Specification, Version 2.1 revision A, December 2005, FlexRay Consortium”. Therein, if the fault detection function of the bus driver detects activity on a connected network branch that is longer than any activity, which is possible in a fault free state, the fault detection function puts the bus driver of the respective network branch into a fail silent node. By this a faulty network branch shall be prevented. Such faulty network branch may be permanently active due to a general hardware fault. However, such faulty network branch may monopolize this network channel and may influence the behavior of the network branches. By using such fault detection, the remaining network branches can still use this network channel for communication in spite of this error, thereby increasing the overall availability of the active star network.
That is, the detection of the faulty network branch in the star network is based on the activity time of the faulty network branch. However, this solution does not prevent the faulty network branch from transmitting wrong information. Usually, an optional bus guardian device is used to detect such wrong information transmitted by a faulty network branch over the active star network. However, such bus guardian is technically complex and a separate component increasing complexity and cost of the whole network.